1. Field of the Invention
The present invention relates to a liquid crystal display. More particularly, the invention relates to a liquid crystal display in which photosensor elements operable to generate light reception data by receiving, at a light receiving surface, incident light which is incident thereon via a liquid crystal layer.
2. Description of the Related Art
Liquid crystal displays have, as a displaying panel, a liquid crystal panel in which a liquid crystal layer is sealed between a pair of substrates. A liquid crystal panel is of, for example, a transmission type in which illuminating light emitted from an illuminator such as a backlight provided at the back side of the liquid crystal panel is transmitted through the liquid crystal panel while being modulated. Then, by the illuminating light thus modulated, display of an image is performed on the front side of the liquid crystal panel.
The liquid crystal panel is, for example, of an active matrix system having a TFT array substrate on which thin film transistors (TFTs) operable to function as pixel switching elements are formed in a pixel area. Here, the thin film transistors are each formed by use of a polycrystalline silicon thin film, for example. In addition, a counter substrate is disposed to be opposed to the TFT array substrate, and a liquid crystal layer is provided between the TFT array substrate and the counter substrate.
In the active matrix type liquid crystal panel, the pixel switching element inputs a potential to a pixel electrode so that an electric field generated between the pixel electrode and a common electrode is impressed on the liquid crystal layer, whereby the orientation of liquid crystal molecules in the liquid crystal layer is changed. By this process, the transmittance for the light transmitted through the pixel is controlled, whereby the light being transmitted is modulated, and an image is displayed through such a modulation.
There has been proposed a liquid crystal panel of this type wherein photosensor elements operable to obtain light reception data by receiving light are incorporated in the pixel area in addition to semiconductor elements such as TFTs functioning as the pixel switching elements (see, for example, Japanese Patent Laid-open No. 2006-3857, hereinafter referred to as Patent Document 1). For instance, PIN (p-intrinsic-n) type photodiodes are integratedly provided as the photosensor elements. Here, the photosensor elements are each formed, for example, by use of a polycrystalline silicon film, like the pixel switching elements.
In the liquid crystal panel as above-mentioned, a user interface function can be realized by utilizing the photosensor elements incorporated therein as position sensor elements. In this type of liquid crystal panel, the need for an external touch panel of a resistor film system or a capacitance system to be separately provided at the front side of the liquid crystal panel is eliminated. As a result, it is possible to reduce the manufacturing cost of the apparatus using the liquid crystal panel and to easily realize reductions in size and thickness of the apparatus.
Further, in the case where a touch panel of the resistor film system or the capacitance system is installed, the quantity of light transmitted through the pixel area may be reduced or interfered by the touch panel, with the result of a lowering in the quality of the image displayed. This problem can be obviated by the above-mentioned configuration in which photosensor elements are incorporated in the liquid crystal panel as position sensor elements.
In this type of liquid crystal panel, for example, the illuminating light emitted from the backlight is transmitted through the liquid crystal panel, and is reflected by an object to be detected such as a user's finger or a stylus pen put into contact with the front surface of the liquid crystal panel, and the visible rays reflected by the object to be detected are received by the photosensor elements incorporated in the liquid crystal panel. Thereafter, based on light reception data obtained through the photosensor elements, the coordinate position where the object to be detected has touched the front surface of the liquid crystal panel is determined, and an operation corresponding to the thus determined position is carried out in the liquid crystal display itself or in an electronic apparatus including the liquid crystal display.
In the case where the coordinate position of the object to be detected is detected by use of the photosensor elements incorporated in the liquid crystal display as above-mentioned, the light reception data obtained through the photosensor elements may contain much noise due to the influence of visible rays contained in the ambient light. In addition, in the case of displaying a dark image such as in black displaying, the visible rays reflected by the object to be detected reaches the light receiving surface of the photosensor element with difficulty, so that it is difficult to receive the visible rays. Thus, there are cases where it is difficult to accurately detect the position of the object to be detected.
For an improvement as to such a trouble, a technique has been proposed in which invisible rays such as infrared rays are used in place of the visible rays (see, for example, Japanese Patent Laid-open No. 2005-275644, hereinafter referred to as Patent Document 2).
Here, the invisible rays such as infrared rays coming from the object to be detected are received by the photosensor elements, to obtain light reception data, and the position of the object to be detected is determined based on the data thus obtained. Especially, human fingers are high in surface reflectance at the infrared wavelengths, and, therefore, use of infrared light is preferable for detection of a human finger.
In this kind of liquid crystal panel, there have been known such liquid crystal displaying modes as the TN (Twisted Nematic) mode and the ECB (Electrically Controlled Birefringence) mode. In addition, liquid crystal displaying modes in which in-plane fields are impressed on a liquid crystal layer, such as the IPS (In-Plane Switching) system and the FFS (Fringe Field Switching) system, have also been known (refer to, for example, Patent Documents 1 and 2).
In each of the liquid crystal displaying modes, a variety of measures have been proposed for improving viewing angle characteristics.
For example, in the in-plane field modes, the pixel electrodes are each formed so as to include a part extending in a direction inclined relative to an x-direction and a y-direction in which the plurality of pixels are arranged in a matrix form. More specifically, a configuration has been proposed in which the pixel electrodes are formed in a shape resembling an angle bracket “<” so as to realize dual-domain pixels (refer to, for example, Japanese Patent Laid-open No. 2007-264231 and Japanese Patent Laid-open No. 2005-338256. With such a configuration, the asymmetry of viewing angle characteristics and gradation reversal which arise from the dielectric anisotropy of liquid crystal molecules are compensated for, and the viewing angle characteristics are thereby improved.